The problem is not yet at epidemic proportions, but the numbers are increasing significantly each year.

Professor Bishop says the disease can be seen everywhere.

"If we look at countries where people cover their skin with cloth because of social or religious reasons - say in the Middle East, there are lots of mums there with the adult form of rickets and children with rickets as well.

"They don't get enough vitamin D form the sunlight and they don't get any in their diet either."

The researchers argue that giving pregnant women vitamin D supplements would be an effective way to combat the problem.

They also emphasise that a short period of exposure to sunlight every day is a good thing - and could stop rickets resurfacing on a major scale.